Tooth decay is usually caused by the bacteria in our mouth that metabolize sugar and other carbohydrates from our food and produce acids that damage the enamel of our teeth. These bacteria live in our mouth and form a sticky film on our teeth called plaque. When we eat sugary or starchy foods, the bacteria in the plaque use them as fuel to produce acids. Over time, these acids can dissolve the minerals in our tooth enamel, leading to cavities and decay. So, it's important to maintain good oral hygiene, limit sugary foods, and visit a dentist regularly to prevent tooth decay. Eating proteinous foods does not directly cause tooth decay, but neglecting oral hygiene after eating such foods can lead to plaque formation and eventually tooth decay.